There are multiple challenges to developing comprehensive HIV prevention programs in developing countries, including: (1) a general lack of consensus on the relative efficacy of interventions, (2) an ever changing and rapidly growing evidence base on intervention efficacy, and (3) a lack of shared standards and terminology for intervention approaches. There has also been a growing interest in promising intervention approaches that target structural and socio-ecological level factors, yet there is little shared theoretical understanding of what constitutes a "structural intervention". As well, many scientific studies published in the peer reviewed literature use common terms for intervention approaches, yet often implement programs very differently. In this proposed study we will systematically review and meta-analyze the impact of 15 key HIV behavioral interventions, and conduct updates on systematic reviews and meta-analyses on 12 additional interventions we have done previously. In addition, intervention case studies will be initiated for those intervention topics listed above in which there is evidence of a lack of consistency across investigators in how they are defining and implementing the intervention. The interventions to be synthesized include: (1) Provider-Initiated HIV Testing and Counseling (PITC), (2) Drug Treatment, (3) Family Life Education, (4) Interpersonal Skills Training (Empowerment), (5) Behavioral Counseling, and (6) Diffusion &Opinion Leader, (7) Free Condom Distribution;(8) Income Generation, (9) Built Environment, (10) Policy Interventions, (11) Social Capital Enhancement, (12) Community Mobilization, (13) Interventions to Enhance Adherence to Antiretroviral Treatment (ART), (14) Interventions designed to Increase Uptake of AIDS Treatment, Mother to Child Transmission (MTCT) Programs, and HIV Testing, and (15) Interventions that Promote Serosorting, (16) Positive Prevention, (17) HIV Voluntary Counseling and Testing (VCT), (18) Peer Education , (19) Family Planning Counseling for HIV-infected Women, (20) Condom Social Marketing, (21) Mass Media, (22) Partner Notification, (23) Abstinence-based Interventions, (24) Needle and Syringe Programs (NSP), (25) Psychosocial Support, (26) Care as Prevention, and (27) Comprehensive School-based Sex Education. PUBLIC HEALTH RELEVANCE: With the dramatic growth in funding for HIV behavioral interventions in developing countries there are multiple initiatives to better allocate of these funds based on evidenced-based standards. Comparative effectiveness studies have been requested by multiple donors and agencies to meet this need. This requires up to date systematic reviews and meta-analyses, as well as careful evaluation of the content of interventions. These will result in improved understanding of which intervention components are proven to be most efficacious, and will advance the field in establishing clear intervention terminology and theoretical constructs. The goal of this study is to provide needed policy and program advice on what is working in HIV prevention based on the strength of evidence from the scientific literature.